Troubleshooting slow braking - now abs?

[Hoffbrohaus]

I have a few other posts & threads trying to figure this out but here's the latest. (already replaced booster, MC o-ring, bled 3x, new pads, checked check valve)

To stop from any speed over 60mph I have to stand on my brakes and it slowly stops. A friend recommended removing the 2 relays in the abs unit to disable it and see if there is a difference. Yes there is. I can now lock up and stop quickly at anytime.

So what does this mean? The ABS diagnostics look good as far as the light being amber and then turning off. I can engage ABS on gravel/dirt. Could there be air in the abs unit? I just don't get how the ABS unit would be preventing hard braking.

[vpilarrt]

If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.

Since the E30 ABS is a 3 channel system (1 for each front wheel and 1 for both rear wheels) it would seem that all 3 solenoids must be closing. I would think that would indicate a control module issue rather than a pump issue as its unlikely that all 3 solenoid would be bad.

I removed the ABS system (working at the time odf removal) from my '89 track car if you're interested in the pump or control module or both.

[RangerGress]

If the anti-lock brake control module senses a wheel is about to lock, based on anti-lock brake sensor data, it closes the normally open solenoid valve for that circuit. This prevents any more fluid from entering that circuit.

Since the E30 ABS is a 3 channel system (1 for each front wheel and 1 for both rear wheels) it would seem that all 3 solenoids must be closing. I would think that would indicate a control module issue rather than a pump issue as its unlikely that all 3 solenoid would be bad.

I removed the ABS system (working at the time odf removal) from my '89 track car if you're interested in the pump or control module or both.

Negative. Google e30 abs ice mode.

When a front sensor locks up the ABS pump pulses that hydraulic line and you can feel the pulsing in the pedal. When one of the rear sensors lock up, the ABS pump doesn't pulse but instead drastically reduces pressure to the rear brakes, and the pedal feels rock hard. That's ABS ice mode and it resets once you get the surprise and alarm off of your face, and your foot off of the brake.

On the track this happens occasionally if you hit the brakes while bounding over a gator. If the timing is such that a rear wheel is airborne then the brake can stop the rear wheel from turning (LSD plays a role here), ABS pump reduces pressure to the rear, brake pedal goes hard, and driver shrieks in horror.

Our car's brakes are very front biased. The slave cylinder creates a 2/3 to 1/3rd bias, and the bias valve, active over 250-300psi depending on who you talk to (light/med foot pressure), adds another 2/3rd to 1/3rd beyond that. As a result, your rear wheels should never lock up before your fronts. I've put hugely more aggressive more pads in the rear vs. front, but I was never able to equalize braking forces on the track. It takes more then pads to make up for all that bias.

[Hoffbrohaus]

Negative. Google e30 abs ice mode.

Thanks for the info. It makes sense to me. I googled e30 ice mode and found a lot of posts on here re: it. My question still is what is causing the ice mode? I read in another post it was the abs controller, he had condensation in it. But then I read it could be the MC (I'm running the 7 series 25mm), and then this from a Porsche forum:

"The best working hypothesis I have seen is that the combination of stiffened suspension, highly sticky tires and aggressive brakes takes the car outside of the parameters of the street-biased ABS system. It isn't designed to see such high deceleration or something and reacts by reducing brake force. Bumps in the brake zone are another contributing factor." Here. So it could be my suspension too?

Then this from SCCA was helpful...
"Most "ice mode" situations can be avoided by squeezing the brakes on rather then stabbing them, so if you regularly encounter this situation your braking style should be the first thing investigated." here.

I'm back to my wild goose chase. I'll start with the scca suggestion first, it's the cheapest even though I have had 3 other people drive it with same results, hard to believe we are all "stabbing" it.

[jlevie]

You could have a bad ABS module or one or more weak/bad rear wheel sensors.

[Tom.]

I don't know if it's relevant or not, but I had all kinds of issues after I swapped in a 25mm MC. Turns out it was an ATE MC, and I was using my stock Girling booster.. apparently the two brands don't work well together? I swapped it out for an early ATE booster and now everything works great.

[Hoffbrohaus]

That is relevant, thanks. I have the 25mm MC too. A local guy is lending me his abs controller if that doesn't work I will try matching ate to ate.

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[Todd Black 88]

Any update?

[Hoffbrohaus]

Nothing really. Pulled the abs computer and I'm waiting for a local guy to lend me his abs cpu. Brakes are great without abs so i haven't been in a rush. Next week I'll try to get that abs cpu.

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[DesertBMW]

Nothing really. Pulled the abs computer and I'm waiting for a local guy to lend me his abs cpu. Brakes are great without abs so i haven't been in a rush. Next week I'll try to get that abs cpu.

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I removed the abs system from my 1989, I'll sell you the whole system for $50 and I am in the valley.

You should first try removing all sensors then cleaning the sensor tips and trigger rings.

[Todd Black 88]

Nothing really. Pulled the abs computer and I'm waiting for a local guy to lend me his abs cpu. Brakes are great without abs so i haven't been in a rush. Next week I'll try to get that abs cpu.

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Bump?

[Hoffbrohaus]

Local guy didn't help. So I have been running no abs still. I'm going to try cleaning the rear sensors. I also notice the e brake is a little tight. When I disengage on a hill the car will roll a little but not much and the brake squeaks. So I'm wondering if the e brake may be telling the rear sensors it's about to lock up so it's like ice mode. I'll adjust the e brake too. Hopefully this week. I tracked it this weekend so abs wasn't my priority. Car was great!

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[Todd Black 88]

Thanks, please keep this thread updated. I have a very similar issue I think.

[brahbarian]

Ha. I thought it was just the nature of the car. My 85 brakes are hard and takes a long time to stop. My 87 brakes fine.
Keep this updated!

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[Todd Black 88]

Any news?